1. Field of the Invention
This invention relates to organic electroluminescence device material (hereinafter referred to as organic EL device material) suitable for organic electroluminescence device (hereinafter referred to as organic EL device) and organic luminous layer of organic electroluminescence device.
2. Description of the Prior Art
The organic EL device is a luminous device having an laminated structure in which a thin film of organic luminous layer containing fluorescent organic compound is sandwiched by a cathode and an anode, producing electroluminescence coinciding with fluorescent spectrum by implanting electrons and electron holes to rejoin them.
As for the structure of the organic EL device, organic EL devices having any one of the following three structures, 1 a structure in which electron hole transporting layer and organic luminous layer are combined, 2 a structure in which electron transporting layer and organic luminous layer are combined and 3 a structure in which organic luminous layer is sandwiched by electron hole transporting layer and electron transporting layer, the respective structures being disposed between the anode and cathode have been known.
FIG. 5 shows a basic composition of an organic EL having the above 1 structure in which electron hole transporting layer and organic luminous layer are combined. On a light transmitting substrate 100 are placed successively a light transmitting anode 101 of ITO (indium tin oxide) or the like, an electron hole transporting layer 102, an organic luminous layer 103 and a cathode 104 of Mg:Ag alloy or the like. Here, the thickness of the electron hole transporting layer 102 and the organic luminous layer 103 which are organic thin films is about 50 nm for both. If minus DC current is applied to the cathode 104 and plus DC current is applied to the anode 101, the organic luminous layer 103 emits light. This emitted light is picked out from the ITO side through the substrate 100. Formation of the respective films are carried out by vacuum deposition.
Here, the above organic luminous layer 103 is made of Alq.sub.3 expressed by Formula 2. Alq.sub.3 is 8-hydroxy quinoline aluminum which is a chelate complex in which 8-hydroxy/quinoline is connected to Al in the center in chelate combination style. The above organic luminous layer 103 made of Alq.sub.3 emits green light of 550 nm in peak wave length. ##STR1##
Here, the above electron hole transporting layer 102 is diamine expressed by Formula 3. ##STR2##
Although the above Alq.sub.3 is a material excellent in terms of luminance, thermal stability and the like as organic EL device material for use in the above organic luminous layer 103, its emitted light is green as described above. To make the organic EL device into multi-color or full color, organic EL device material (phosphor) emitting blue and red colors having full luminance and practical purity is necessary in addition to organic EL device material emitting green light.
As organic EL device material producing blue light emission, azomethyn zinc complex Zn (1AZM-Hex) expressed by Formula 4 and benzoxazole zinc complex Zn(OXZ).sub.2 expressed by Formula 5 have been known. ##STR3##
Although there are a number of organic materials producing blue fluorescence, the number of those that can be used as organic EL material is small. The reason is that the following conditions are not satisfied.
(1) Fluorescence of thin film must be blue color having a purity allowing its practical use.
(2) The thin film is thermally stable so that it is not coagulated despite a long-term storage.
That is, if the melting point is low, the thin film is subjected to physical changes such as crystallization due to heat so that crevice may occur and leak current flows thereby leading to deterioration. Thus, as the organic EL material, material having the same property as the aforementioned Alq.sub.3 (melting point: 418.degree. C.) conventionally reputed to be excellent or material which has a higher melting point and is thermally stable is desirable.
(3) In organic EL device having the above construction 1 in which the electron hole transporting layer and organic luminous layer are combined, energy gap with the electron hole transporting layer is not reduced so that exciplex is not formed. If exciplex is formed, sometimes EL luminance becomes not blue but green.
(4) Electrons and electron holes can be implanted so that carriers can move.
Upon consideration of the conventional organic EL device material emitting blue light from the above point of view, although azomethyn zinc complex Zn (1AZM-Hex) in Formula 4 described above for example produces a peak wave length in fluorescence of 450 nm emitting blue light, its melting point is 353.degree. C. which is lower than 418.degree. C. of Alq.sub.3. Further, benzoxazole zinc complex Zn (OXZ).sub.2 in Formula 5 produces a peak wave length in fluorescence of 493 nm emitting bluish green light and its melting point is 354.degree. C. which is lower like Formula 4.